Java 9嵌套（分层或父/子）模块 [英] Java 9 Nested (Hierarchical or Parent/Child) Modules

问题描述

是否可以在Java 9中创建基于继承的（或嵌套的）模块？

Is it possible to create inheritance-based (or nested) modules in Java 9?

这样的事情：

module a
   |
   ├── module a1
   |   
   └── module a2

在这个例子中， a1 和 a2 模块是 a 的子项。

In this example, both the a1 and a2 modules are children of a.

如果我导入其中一个子模块，我将获得父模块的功能（ a ）以及该子模块中定义的任何功能。也就是说，我可以导入 a1 ，并明确获得对 a 和 a1 （但不是 a2 ）。

If I import either of the child modules, I would get the functionality of the parent (a) along with any functionality defined in that child. That is, I could import a1, and explicitly gain access to the functionality of both a and a1 (but not a2).

两者 a1 和 a2 是 a ，可以访问<$的所有包c $ c> a ，无需向他们公开 a 的包裹。

Both a1 and a2 are an a, and can access all of the packages of a, without having to expose the packages of a to them.

推荐答案

您可以通过的组合模仿您要求的内容和导出到语法：

You can emulate what you asked for with a combination of requires transitive and exports to syntax:

• 需要传递 ：指定导入此模块将固有地导入另一个模块。您可以使用它来确保 a1 和 a2 导致 a 要导入。


• 导出到：这样您就可以将功能导出到特定模块;这将允许您让 a 授予 a1 和 a2 公开出口会很危险的功能。



• requires transitive: Specifies that importing this module will inherently import another module. You can use this to ensure that a1 and a2 cause a to be imported.
• exports to: This will let you export functionality to a specific module only; this will allow you to let a give access to a1 and a2 functionality that would be dangerous to have publicly exported.

所以，例如：

module a {
    exports com.internal to a1;
    exports com.internal to a2;
}

module a1 {
    requires transitive a;
}

module a2 {
    requires transitive a;
}

在这种情况下，如果消费者依赖 a1 ，它们本来就依赖于 a （从而获得两者的效用），以及 com.internal 包，虽然可供 a1 供内部使用，但消费者无法在外部看到。

In this case, if a consumer depends on a1, they will inherently depend on a (thus gaining the utilities of both), and the com.internal package, while visible to a1 for internal use, will not be externally visible to the consumer.

这不是你要求的。 a1 不 a 。此外， a1 不能 a ; JLS 不允许对于出口中的通配符（IE： exports * to a1 ，仍然不会使 a1 a 但是从实用的角度来看会更接近它，​​并且模块中不存在允许它的其他语法。

It is not quite what you asked for. a1 is not an a. Further, a1 can not be made to be an a; the JLS does not allow for wildcards in exports (IE: exports * to a1, which still wouldn't make a1 an a but would bring it closer from a pragmatic perspective), and no other syntax exists in modules to allow for it.

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